Abstract: Several established cancer treatments take advantage of the hypersensitivity of cancer cells to DNA damage by inducing genome-wide damage to cellular DNA. However, tumors often evolve resistance to DNA-damaging chemotherapeutics by elevating the activities of DNA repair pathways, becoming dependent on specific repair activities for survival. These observations make therapeutics that selectively target individual DNA repair proteins, especially those involved in therapeutic resistance, highly valuable. Inhibitors that block activity of the DNA repair protein poly-ADP ribose polymerase are one example of specific repair inhibitors that show great promise as chemotherapeutics. This proposal extends this approach to target a novel chemotherapeutic DNA repair pathway by developing small-molecules that block the critical interface linking two DNA repair complexes known to be involved in tumor chemotherapeutic resistance -- the Fanconi Anemia complex and the Bloom Dissolvasome. X-ray crystallographic, biochemical, and cell biological approaches have revealed the critical nature of this higher-order complex for cellular genomic stability and its promise as a novel therapeutic target. In addition, I have developed an excellent high throughput screening ready strategy that has already identified a small number of inhibitors in a pilot study. In this proposal, I will carry out a large-scale high- throughput chemical screen to identify protein-protein interaction inhibitors that disrupt the formation of the Fanconi Anemia-Bloom Dissolvasome supercomplex. Biochemical, structural, and cellular approaches will be used to assess the potency and mechanisms of action of the inhibitors and to drive rational lead improvement. The chemotherapeutic potential of the lead compounds will be determined by measuring their effects on the specific types of DNA damage repaired by the supercomplex and by assessing whether they selectively inhibit growth of human cancer cell lines as monotherapies and as adjuvants with clinical chemotherapeutics.